1. Field of the Invention
The present invention relates to a system for lubricating a hand-held type 4-cycle engine used as a power source mainly for a trimmer or a chain saw.
2. Description of the Related Art
The conventional hand-held type engine widely used in these applications is a 2-cycle engine capable of exhibiting a lubricating function in any operational attitude of the engine such as inclined and sideways-fallen attitudes.
However, as such a hand-held type engine, it is desirable to use a 4-cycle engine from the viewpoint of an exhaust emission control. In the 4-cycle engine, however, it is necessary to store an oil exclusively used for lubrication. Therefore, if the 4-cycle engine is used as the hand-held type engine, it is necessary to reliably lubricate various portion of the engine in any operational attitude of the engine.
Accordingly, it is one object of the present invention to provide a 4-cycle engine lubricating system capable of satisfying the above requirements for use in hand-held tools.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a system for lubricating a 4-cycle engine, comprising: an oil reservoir chamber which stores a lubricating oil therein and has an oil mist producing means contained therein for producing an oil mist from the lubricating oil; a crank chamber having a crank portion of a crankshaft contained therein; and a valve-operating chamber having a valve-operating device contained therein, the oil reservoir chamber, the crank chamber and the valve operating chamber being provided in an engine body, the oil reservoir chamber and the crank chamber being in communication with each other through a through-hole above an oil level in the oil reservoir chamber, the crank chamber and the valve operating chamber being in communication with each other through a control valve which is opened upon rising of the pressure in the crank chamber and closed upon reduction of the pressure in the crank chamber, the valve-operating chamber being substantially in communication at its upper portion with the atmosphere and at its bottom portion with the oil reservoir chamber through an orifice, and the following expression is established during operation of the engine;
Pcxe2x89xa6Po less than Pv
wherein Pc is a pressure in the crank chamber; Po is a pressure in the oil reservoir chamber; and Pv is a pressure in the valve-operating chamber.
With the first feature of the present invention, in any inclined state of the engine, the oil mist can be constantly circulated to the oil reservoir chamber, the crank chamber, the valve-operating chamber and the oil reservoir chamber and the oil liquified in the valve-operating chamber can be circulated to the oil reservoir chamber by utilizing the magnitude of the differences between the pressures in the chambers, thereby insuring a good lubricating state. Moreover, an expensive oil pump is not required and hence, this lubricating system is convenient even in a respect of cost.
According to a second aspect and feature of the present invention, in addition to the above first feature, the system further includes an uppermost chamber which occupies a position above the valve-operating chamber and communicates with the valve-operating chamber through an orifice and also communicates with the oil reservoir chamber or the crank chamber through an oil passage, and the following expression is established during operation of the engine:
Pcxe2x89xa6Poxcx9cxe2x89xa6Pt less than Pv
wherein Pt is a pressure in the uppermost chamber.
With the above second feature of the present invention, not only the circulation of the oil mist but also the circulation of the oil liquified and accumulated in the uppermost chamber can be reliably performed, and a good lubricating state can be insured.
According to a third aspect and feature of the present invention, in addition to the above first feature, the oil mist producing means comprises an oil slinger which is rotated by the crankshaft to agitate and scatter the lubricating oil in the oil reservoir chamber at all times irrespective of the inclined state of the engine.
With the third feature of the present invention, the oil mist can be reliably produced in the oil reservoir chamber by the rotation of the oil slinger in any operational attitude of the engine and moreover, the structure of the oil slinger is relatively simple.
According to a fourth aspect and feature of the present invention, in addition to the first or second feature, the control valve comprises a one-way valve of a pressure responsive type.
With the fourth feature, the one-way valve can be opened and closed in operative association with the pressure pulsation in the crank chamber to transfer the oil mist from the crank chamber into the valve-operating chamber and to maintain the crank chamber in an averagely negative pressure state. Particularly, the sealing function is good during closing of the one-way valve and hence, the lubricating system is effective for an engine rotating at relatively lower speeds.
According to a fifth aspect and feature of the present invention, in addition to the first or second feature, the control valve comprises a rotary valve which is opened upon the lowering movement of a piston operatively associated with the rotation of the crankshaft and closed upon the elevating movement of the piston.
With the fifth feature, the rotary valve can be opened and closed in mechanically operative association with the rotation of the crankshaft to transfer the oil mist from the crank chamber into the valve-operating chamber and to maintain the crank chamber in an averagely negative pressure state. Particularly, a deviation in timing of opening and closing of the rotary valve cannot be produced and hence, the lubricating system is effective for a relatively lower-speed rotated type engine.
According to a sixth aspect and feature of the present invention, in addition to the fifth feature, the opening duration of the rotary valve is approximately 180xc2x0 in terms of a crank angle, and the start point of opening of the rotary valve is set in a range of from a middle point between top and bottom dead centers of the piston to a lowering-piston position of 45xc2x0 of the piston in terms of the crank angle.
With the sixth feature of the present invention, the discharge of a positive pressure from the crank chamber into the valve-operating chamber can be effectively performed by utilizing an inertial effect of a gas during rotation of the engine at a high speed. Therefore, the transferring of the oil mist and insuring of the negative pressure state of the crank chamber can be more reliable.
The above and other objects, features and advantages of the invention will become apparent from the following description of preferred embodiments taken in conjunction with be accompanying drawings.